According to the Traffic Safety White Paper (published by the Ministry of Land, Infrastructure, Transport and Tourism of Japan), the number of traffic accidents has maintained a decreasing tendency in recent years, but it is notable that the accidents involving pedestrians account for a largest part of the number. With the aim of protecting pedestrians from traffic accidents, research and development efforts have been directed to the use of a pedestrian-vehicle communication system as a part of a traffic safety assist wireless communication system of the ITS (Intelligent Transport System).
In a pedestrian-vehicle communication system, each traveling object (such as a pedestrian and a vehicle) carries a pedestrian-vehicle communication device to acquire information (current positions, traveling directions, traveling speeds, etc.) from other traveling objects (such as pedestrians and vehicles) each carrying a pedestrian-vehicle communication device, and broadcasts information on itself. Based on the information received from other pedestrian-vehicle communication devices and the information on itself, each traveling object can prevent traffic accidents.
However, since the broadcast of information by each traveling object is performed on one channel using the frequency of 700 MHz allocated for the ITS, in a crowded area or in a busy street, communication difficulties and communication delays are likely to occur due to line congestion. In order to mitigate the influences of such line congestion, a system has been proposed wherein, when a plurality of pedestrian-vehicle communication devices carried by pedestrians (pedestrian terminal devices) are located close to each other, a pedestrian terminal group is formed, and a pedestrian terminal device representing the group (principal terminal) is designated so that the principal terminal performs a pedestrian-vehicle communication with the pedestrian-vehicle terminal devices carried by vehicles (in-vehicle terminal devices) by representing the group. See JP4876628B2 and JP2011-253403A, for example.